The present invention relates in general to that type of speedboat which is commonly termed a hydroplane and of the limited or unlimited class. The currently most successful types of such boats are generally referred to as three-point suspension boats, indicating that, at higher speeds, the boat is supported on the water at the propeller and at the trailing ends of the two side sponsons. With boats of such attitudes to the water, most of the underside of the boat is exposed to and is being contacted by relatively passing air. In bad weather, such as when the wind is substantial and is gusty and the water surface is rough, the action of the relatively passing air on the large, exposed underside of such a boat is such as to provide for a very unstable boat. The stability of such a boat is often reduced to a minimum and requires the slackening of speed to a point below that considered acceptable under racing conditions. Also, when such boats are operated in rough weather, they often jump or leap from one wave crest to the next. This causes the load on the driven propeller and connected power plant to move from maximum to minimum and vice versa and thus provides maximum strains on such equipment.
As hereinafter discussed in greater detail, I provide a boat which is supported on a water surface on five stepped planing surfaces. A main body portion has a stepped planing surface on its underside and which surface is located well forward of the center of gravity of the boat and provides a supporting surface for the front end portion of the boat. Two side sponsons are connected by a wing structure with the main body portion. These side sponsons are disposed parallel to each other and parallel to the main body portion. Each side sponson has on its underside, two stepped planing surfaces, a forward one located forward of the center of gravity of the boat and a rearward one located rearwardly thereof and extending to the rear of the boat. Thus, the boat has five stepped planing surfaces on which it may be supported on a water surface. The wing structure interconnecting the side sponsons and the main body portion tapers to a sharp, leading, forward edge and also tapers to a thin, trailing edge. During higher speeds of the boat, the said forward edge is about twice as far from the water surface as the said trailing edge; the boat is supported on said five stepped planing surfaces; the propeller is turning with about two-thirds thereof below the water surface; and the boat is supported by the relatively passing air below the wing structure. The side sponsons prevent such relatively moving air from escaping sidewise and thus, the said air is compressed beneath the wing structure. This compressed air provides the lifting force supporting most of the weight of the boat and its contents. If rough water should lift the boat from the water surface, the effective force of the compressed air will be lessened and the boat will again rest on the water and resume a proper and stable attitude. As the construction provides for an attitude of the boat in the water with the bow on the water, a steering rudder is provided at the bow rather than at the stern of the boat. In order that the stern shall follow the bow portion during turns rather than slipping sidewise, fins having a substantial surface disposed longitudinally of the boat and vertically are provided. Also, a fin is disposed close to the wash side of the propeller to counterbalance the torque or the tendency of the aft end of the boat to move sidewise in a given direction in response to the rotation of the propeller in a given direction.